Thermal relay,double pole,normally-open and normally-closed



June 23, 1970 M. D. PATRICHI 3,517,366

THERMAL RELAY, DOUBLE POLE, NORMALLY-OPEN AND NORMALLY-CLOSED Filed May 9, 1968 I JGJ FIG. 3

I I I I 1 I INVENTOR.

I QZfl/A/ 0247210 216% {A TTOPNBL United States Patent 3,517,366 THERMAL RELAY, DOUBLE POLE, NORMALLY- OPEN AND NORMALLY-CLOSED Mihai D. Patrichi, 9750 De Soto Ave., Chatsworth, Calif. 91311 Filed May 9, 1968, Ser. No. 727,769 Int. Cl. H01l1 71/20 U.S. Cl. 337-148 Claims ABSTRACT OF THE DISCLOSURE A thermal relay, having a fuse-restrained spring-loaded plunger which, when released by melting of the fuse, will effect closing of a set of normally open contacts and opening of a set of normally closed contacts.

SUMMARY OF THE INVENTION This invention provides a current sensitive thermal relay of small dimensions, a portion of which has the characteristics of a fuse and is included in a load circuit which, when overloaded, will raise the temperature thereof to the critical range when the fuse will melt, releasing a spring loaded plunger that switches the contacts of another portion of the relay providing normally-open and normally-close contacts, in double-pole circuits which are separate from the fuse circuit; and envelope structure consisting of a tubular housing of high temperature resistant glass (e.g. Pyrex) and headers sealing the respective ends of said housing; a pair of terminals extneding through and. sealed in the fuse circuit end header; and two pairs of terminals extending through and sealed in the doublepole circuits end header.

BACKGROUND OF INVENTION Thermal relays of small dimensions, sealed in glass and triggered 'by rupture of a fusible element, are disclosed in the following prior patents: 2,934,635, Patrichi, Apr. 26, 1960, Temperature Sensitive Normally-Open Relay; 2,974,761, Patrichi, Mar. 14, 1961, Electrical Component With Improved Metal-to Glass End Sealing Mechanism; 2,934,622, Massar, Apr. 26, 1960', Thermal Relay, Normally Closed, With Guillotine for Opening.

A switch having normally open and normally closed contacts which, upon actuation by detonation of an explosive squib, are reversed to closed and open condition respectively, is shown in Pat. No. 2,999,912, Kincaid, Sept. 12, 1961. The construction shown is bulky, however, and does not lend itself to hermetic sealing. The present invention improves this type of relay, with objects as stated more fully hereinafter.

DESCRIPTION The general object is to provide an improved current sensitive, double pole-single throw, normally-open, normally-closed relay of this type, suitable for use under high requirement conditions of wide temperature range, jetpropelled missiles and space vehicles and in other similar structures. A particular object is to provide such a relay embodying an improved miniaturized construction hermetically sealed against moisture, salt spray, fungus, etc. A further object is to provide such a thermal relay embodying electrical parts mounted in a glass envelope pro viding full visibility of the working parts thereof.

These and other objects will become apparent in the following detailed description, taken with the accompanying drawing, in which:

FIG. 1 is a longitudinal sectional view of a relay embodying the invention, the glass housing element being shown in section and remaining parts being shown in elevation;

"ice

FIG. 2 is an axial sectional view of the same, taken in a plane at right angles to the plane of FIG. 1;

FIG. 3 is a transverse sectional View taken on line 3--3 of FIG. 1;

FIG. 4 is a transverse sectional view taken on the line 44 of FIG. 1; and

FIG. 5 is an end view showing the two sets of contact terminals, the normally-open set and the normally-closed set.

Referring now to the drawing in detail, I have shown therein, as an example of one form in which the invention may be embodied, a double-pole, one normally-open switch and one normally-closed switch, fuse actuated thermal-relay embodying, in general, an envelope structure comprising a cylindricmal tubular glass housing 10 and headers 11 and 12 secured in and sealing the respective ends of housing 10 to provide therewith a sealed envelope; together with relay parts within the envelope, including a plunger 13 slidably mounted within the housing 10, a coil spring 14 for projecting the plunger 13 to a position in which its chisel-nose cylindrical projection 15 operates to sever a fine wire bridge 16 of the normallyclosed terminals 17 of header 12 and subsequently plugs its conical metal ring contact head 18 between the normally-open contacts of header 12; and a fuse element 19 anchored between the pluger 13 and a pair of anchor loops 20 mounted in the header 11, whereby the plunger 13 is normally held in a retracted position but will be released upon melting of the fuse element 19 when subjected to overload, thereby causing the plunger 13 to be springprojected and contact switching to be performed as described.

The headers 11 and 12 each include a metal mounting ring 21 of L-section consisting in a radial flange and an open collar projecting axially from the inner margin of the flange into a respective end of housing 10. Mounting solder rings are soldered at the radial flanges of headers 11 and 12 to the ends of housing 10, previously covered with metal as hereinafter described, to provide a very secure pneumatically-sealed connection. Each header 11 and 12 includes a plug 27 of glass (e.g. Pyrex) fused into the collar thereof. Terminal rods or wires 17, 22 and 23 are fused into cylindrical bores in respective glass plugs and project therethrough into the respective ends of the sealed chamber within housing 10.

The ends of terminals 23 of header 11 are formed with the loops 20 constituting the spaced anchors for attaching the fuse ends. The loops 20 are disposed in parallel planes equally spaced on opposite sides of and parallel to the longitudinal axis of the relay. Each loop 20 is formed integrally on the end of a respective terminal 23, the latter extending entirely through the plug 27 of header 1 1 in one of the bores thereof. The loop embodies two straight parallel legs, one of which is a linear extension of the terminal and the other of which is a return bend extending fully or part way through an adjacent bore of the plug 27. The terminal and the leg of the loop are fused to the glass walls of their respective bores. Each loop is of curved arch form bridging between and integrally joining the two legs of the loop to constitute the fuse terminals which are disposed in substantially parallel relation equally spaced from opposite sides of the relay axis.

The four terminals 17 and 22 of header 12 are circumferentially oflset (e.g. in respective axial planes at to one another). They consist of lengths of wire extended through and mounted in the respective header, and they have respective inner end portions of dilferent lengths, projecting into the interior of the envelope, one pair of diagonally opposed terminals being normally closed by a frangible bridge conductor 16, and the other pair being normally-open contacts. The glass plugs of both headers 11 and :12 have two pairs of bores disposed respectively parallel to the longitudinal axis of the relay, spaced apart circumferentially at 90 spacing and at equal radial spacing from the axis. All four terminals of header 12 are fused to the glass walls of their respective bores of the glass plug. The L-section mounting ring and the terminals of both headers 11 and 12 are drawn of a corrosion resistant metal such as Kovar (an alloy of iron, nickel and cobalt) having substantially the same coefficient of thermal expansion as the glass housing and the glass plugs of the respective headers.

The inner portions of the diagonally opposed terminals 22 (the normally-open contacts) are longer and bent so as to diverge at 24 toward the glass wall of the envelope 10, with end portions 25 almost touching it and parallel to the longitudinal axis of the relay. The ends 25 are bevelled at 26 to bring to a stop and mate with the conical contact head 18 of the plunger 16 in its movement under the action of spring 14, thus closing electrically the normally-open contacts.

Plunger 13, with the exception of its metal contact ring 18 for closing the normally-open contacts, is of molded insulating material, preferably a thermosetting plastic material. The contact ring 18 is of a non-corrosive metal such as silver or silver-plated brass, and is securely anchored in the plastic material of plunger 13 and centered at the axis thereof. In the rear end of the plunger 13 is a cylindrical axial recess 30 which is traversed diametrically by a metal anchor pin 31. The bight of fuse link 19 is looped around the pin 31 and a substantial portion of the length of fuse link 19 is received in the recess. The respective ends of the fuse link 19 are wrapped around and brazed to each of the terminal loops of header 11 projecting into the interior of the envelope. The frangible conductor 16 stretched between the ends of the normally closed terminals of header 12 is brazed in slots cut in the ends of the terminals, and is of a soft good conductor wire as of silver or copper.

In order to insulate electrically the fuse link 19 and the terminal loops 20 of header 11 from coil spring 14, an insulating grommet 33 is added, having an L-section whose flange rests between the end of the coil spring and the inner glass face of header 11 with the barrel part of the grommet separating the spring from the fuse and its terminals. As the means for bonding the mounting rings of headers 11 and 12, each one to the respective end of glass housing 10, I utilize the multiple layer bonding connection disclosed fully in my Pat. No. 2,974,761, of Mar. 14, 1961, for Electrical Component With Improved Metal-to-Glass End Sealing Mechanism, filed June 4, 1958. Briefly, such bonding connections (indicated generally by numeral 35) comprise in general coatings of silver plated upon the mounting rings of headers 11 and 12, and coatings of silver solder sweated into the interstices between the coated mounting rings 21 on the one hand and the coated surfaces of the respective ends of housing 10 on the other hand.

I claim:

1. In a thermal relay:

a tubular housing;

headers mounted in the respective ends of said housing;

a first pair of terminals mounted in and projecting through one of said headers;

second and third pairs of terminals mounted in and projecting through the other header in circumferentially-spaced positions, with the terminals of the second pair projecting into the housing in a plane transverse to the plane of the third pair and having a pair of normally-open contacts providing a portion of a normally-open circuit;

a frangible bridge providing a conductive connection between said third pair of terminals to provide a portion of normally-closed circuit;

a plunger axially slidable in said housing, said plunger having (a) a projection positioned to sever said bridge upon axial movement of said plunger in a projection stroke,

whereby to open said normally-closed circuit;

(b) a contact head positioned to engage and provide a conductive connection between the contacts of said second pair of terminals so as to close said normally open circuit as a result of said plunger stroke;

(c) a fuse element normally providing a conductive connection between said first pair of terminals in a load circuit to be protected, said fuse element providing an anchoring connection between said plunger and said one header, normally restraining said plunger in a retracted position away from said bridge and normallyopen contacts;

(d) and a coil spring engaged under compression between said one header and said plunger to project the latter in said stroke in response to failure of said fuse element when subjected to overload in said load circuit, whereby to open said normally-closed circuit and to close said normally-open circuit;

said projection, when at rest, being spaced from said bridge a distance which is less than the distance from said contact head to said normally-open contacts so as to first sever said bridge and open said normally-closed circuit and to subsequently engage said normally-open con.- tacts and close said normally-open circuit.

2. A relay as defined in claim 1, wherein said projection is of insulating material and of wedge shape, having a leading edge disposed in crossed relation to said bridge at the center thereof.

3. A relay as defined in claim 1, wherein said plunger comprises a body of insulative material and said contact head comprises a conductive ring mounted on the frontal end of said plunger body; said projection being an integral, reduced diameter forward extension of said plunger projecting through said ring.

4. A relay as defined in claim 1, wherein said plunger comprises a body of insulative material and said contact head comprises a conductive ring mounted on the frontal end of said plunger body;

said ring having an internal axial flange embedded in said insulative material.

5. A relay as defined in claim 1, wherein said plunger comprises a body of insulative material having a periphery loosely fitted within said housing for guiding the plunger in said stroke,

and said projection comprises a shaft integral with said plunger and of reduced diameter projecting forwardly from the frontal end of said body radially inwardly of the contact areas of said head and having a forward chisel edge in crossing relation to said bridge for severing said bridge.

6. A relay as defined in claim 1, wherein said plunger comprises a body of insulative material having a periphery loosely fitted within said housing for guiding the plunger in said stroke and having an integral neck of reduced diameter projecting for-wardly on its axis;

said contact head comprises a conductive ring surrounding and mounted on said neck; said projection comprising an enlarged integral forward egtension of said neck and terminating in a chisel e ge;

said head consisting of a metal ring surrounding said reduced neck and engaged between said plunger and said projection.

7. A relay as defined in claim 1, wherein said contact head and normally-open contacts have respective contact surfaces in aligned, substantially parallel relation such that said head is wedged between said normally-open contacts upon projection of the plunger;

and wherein said second pair of terminals includes portions extending through said other header in positions spaced radially inwardly from the inner wall of said housing, and other portions projecting into said housing in diverging relation and in close proximity to said housing inner wall at their ends, whereby spreading of said normallly-open contacts will be limited by abutting engagement of said ends with said housing wall.

8. In a miniature thermal relay:

a hermetically sealed envelope comprising a tubular barrel of high temperature glass and a pair of headers closing and sealing the respective ends thereof, each of said headers comprising a cylindrical center plug of high temperature glass corresponding to that of said barrel in expansion characteristics and a mounting ring of a metal alloy that is matched to said glass parts in expansion characteristics, interposed between and bonded to the respective glass parts at each end of the envelope, said mounting ring being of L-section, including a fiat radial flange bonded to a respective end of said barrel by coatings of silver paste fused to barrel ends, coatings of copper plated over fused silver coatings, coatings of silver plated upon mounting rings and solder sweated into the interstices for sealing parts together, and a cylindrical collar of said ring extending from the inner margin of the flange into a respective end of said barrel and radially spaced therefrom by an annular cylindrical space;

a first pair of terminals mounted in and projecting through one of said headers;

second and third pairs of terminals mounted in and projecting through the other header in circumferentially-spaced positions, with the terminals of the second pair projecting into the housing in a plane which is transverse to the plane in which the third pair of terminals lie and having a pair of normally-open contacts providing a portion of a normally-open circuit;

a frangible bridge providing a conductive connection between said third pair of terminals to provide a portion of a normally-closed circuit;

a plunger axially slidable in said housing, said plunger having (a) a projection positioned to sever said bridge upon axial movement of said plunger in a projection stroke,

whereby to open said normally-closed circuit;

(b) a contact head positioned to engage and provide a conductive connection between said second pair of terminals so as to close said normally-open circuit as a result of said plunger stroke;

a fuse element normally providing a conductive connection between said first pair of terminals in a load circuit to be protected, said fuse element providing an anchoring connection between said plunger and said one header, normally restraining said plunger in a retracted position away from said bridge and normally-open contacts;

and a coil spring engaged under compression between said one header and said plunger to project the latter in said stroke in response to failure of said fuse element when subjected to overload in said load circuit, whereby to open said normally-closed circuit and to close said normallyopen circuti;

and an insulating grommet of L-section, insulating the coil spring from the metal ring of the header and the fuse terminals.

9. A relay as defined in claim 8, wherein said plunger comprises a body of insulative material having a periphery loosely [fitted within said housing for guiding the plunger in said stroke,

said contact head comprises a conductive ring mounted on the frontal end of said body,

and said projection comprises a shaft of reduced diameter projecting forwardly through said ring from said frontal end.

10. A relay as defined in claim 8, wherein said plunger comprises a body of insulative material having a periphery loosely fitted within said housing for guiding the plunger in said stroke,

and said projection comprises a shaft of reduced diameter projecting forwardly from the frontal end of said body through and radially inwardly of the contact areas of said head,

said projection being an integral part of said insulative body.

References Cited UNITED STATES PATENTS 3,202,953 8/1965 Bosworth et a1. ZOO-51.09 XR 3,155,800 11/1964 Denton ZOO-61.00 XR 2,934,625 4/1960' Patrichi 337-148 2,974,761 3/1961 Patrichi 287-189.365 2,934,622 4/1960 Massar 337-157 2,683,201 7/1954 Miller et al. 337-148 1,478,481 12/1923 Maple 337-148 BERNARD A. GILHEANY, Primary Examiner D. M. MORGAN, Assistant Examiner US. Cl. X.R. 337-157 

